1. Field of the Invention
This invention relates to watertight cameras for underwater photography.
2. Description of the Prior Art
Conventional watertight cameras have their finders and transparent protectors for their finders oriented so that the optical axis of the finder is parallel to the optical axis of the photographic objective, or intersects the latter at infinity. Though its parallax is not very appreciable for ordinary in-the-air photographic situations, this finder arrangement cannot be applied to underwater photography without problems. Because an object to be photographed underwater often lies at a relatively short distance of about 1 meter, a large parallax between the optical axes of the finder and the objective appears. Accordingly, when the photographer relies on the finder in placing an image of the object at the center of the viewfield, the photograph actually taken will be found to have the object image at or near one of the corners of the picture format.
An attempt has been made to overcome this drawback by inclining the optical axis of the finder to intersect that of the photographic lens at a distance of about 3 meters. This method relieves the problem to some extent, but does not perfectly improve the system.
The strobe built in watertight cameras has its reflector and protector pointing toward the object to be photographed in parallel with the optical axis of the objective. There is no problem in using this flash illumination for in-the-air photography. With underwater photography for an object at a relatively short distance (of about 1.5 meters), because the center axis of the path of rays from the strobe is deviated considerably from the axis of the strobe, only a marginal portion of the path of flash light rays is useable, causing flash illumination on the object to be insufficient or uneven. Therefore, under-exposed photographs will be taken, and the right and left hand margins of the picture frame will differ greatly in exposure from each other.